1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a main pole and a shield.
2. Description of Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of a recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head section having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head section having an induction-type electromagnetic transducer for writing are stacked on the top surface of a substrate. The write head section includes a main pole that produces a write magnetic field in the direction perpendicular to the plane of a recording medium. The main pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces a recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a generally constant width. To achieve higher recording density, it is required that the write head section of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of a recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium.
Here, the side of the positions closer to the leading end relative to a reference position will be defined as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be defined as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erasure). For achieving higher recording density, it is necessary to prevent adjacent track erasure.
Providing a write shield near the main pole is effective for preventing adjacent track erasure induced by the skew mentioned above and increasing the recording density. For example, U.S. Pat. No. 6,954,340 B2 and U.S. Patent Application Publication No. 2005/0128637 A1 each disclose a magnetic head including a write shield having an end face that is located in the medium facing surface to wrap around an end face of the main pole.
A magnetic head including a write shield is typically provided with one or more return path sections for connecting the write shield and part of the main pole away from the medium facing surface to each other. The write shield and the one or more return path sections have the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, so as to prevent the magnetic flux from reaching the recording medium. The write shield and the one or more return path sections also have the function of allowing a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole. Thus, the magnetic head including the write shield makes it possible to prevent adjacent track erasure and allows a further improvement of the recording density.
U.S. Pat. No. 6,954,340 B2 and U.S. Patent Application Publication No. 2005/0128637 A1 each disclose a magnetic head including, as the aforementioned one or more return path sections, a return path section located on the trailing side relative to the main pole and a return path section located on the leading side relative to the main pole.
Now, the configuration of the return path section located on the leading side relative to the main pole (hereinafter, referred to as the leading return path section) will be contemplated. In a magnetic head, the read head section and the write head section stacked on the top surface of the substrate are typically located on the trailing side relative to the top surface of the substrate. In this case, the leading return path section is interposed between the main pole and the top surface of the substrate. The main pole and the leading return path section define a space through which a portion of a coil passes. In such a magnetic head, the leading return path section is typically configured to have a first layer, a second layer formed on the first layer at a position near the medium facing surface, and a third layer formed on the first layer at a position away from the medium facing surface. The second layer connects a part of the first layer located near the medium facing surface to the write shield. The third layer connects a part of the first layer located away from the medium facing surface to a part of the main pole located away from the medium facing surface.
In the magnetic head shown in FIG. 8 of U.S. Patent Application Publication No. 2005/0128637 A1, a return pole located on the leading side relative to the main pole corresponds to the aforementioned first layer, a shorting shield located on the leading side relative to the main pole corresponds to part of the write shield and the aforementioned second layer, and a back via located on the leading side relative to the main pole corresponds to the aforementioned third layer.
In the typical configuration of the leading return path section described above, the second layer is much longer in the direction of travel of the recording medium than in the direction perpendicular to the medium facing surface, and an end face of the second layer is exposed over a large area in the medium facing surface. When the second layer has such a configuration, part of the magnetic flux captured into the second layer from a part of the end face of the second layer located near the end face of the main pole may leak from another part of the end face of the second layer toward the recording medium. This may result in the occurrence of adjacent track erasure.
Furthermore, when the leading return path section has the typical configuration described above, heat generated by the coil may cause expansion of the second layer and an insulating layer surrounding the coil, and thereby cause the end face of the second layer to protrude toward the recording medium. The protrusion of the end face of the second layer causes the end face of the main pole and an end of the read head section located in the medium facing surface to get farther from the recording medium, and this may result in degradation of the read and write characteristics.